Restore support for Java 8

[reta]

Description

Restore support for Java 8

Issues Resolved

Closes #156

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[dblock]

YES! Let's add CI.

[reta]

YES! Let's add CI.

Thanks @dblock ! Working on it :)

[reta]

@dblock @VachaShah ended up with the following change:

• the opensearch-java baseline is back to 1.8 (since RestClient is also back to 1.8)
• the integration tests heavily rely on OpenSearch core test framework (it could not be switched to JDK 8), so these tests need JDK-11 baseline, the solution here (one of) is to split tests into src/test/java and src/test/java11
• the Gradle build uses grgit-gradle 5.x that also needs JDK-11 baseline so we cannot build with JDK 8 sadly (it explains why GA/CI has no JDK 8 in matrix)

[dblock]

• the Gradle build uses grgit-gradle 5.x that also needs JDK-11 baseline so we cannot build with JDK 8 sadly (it explains why GA/CI has no JDK 8 in matrix)

I think this should be a blocker. Can we downgrade? We need at least some CI on JDK8, anything even a basic integration test would be enough.

[dblock]

I would be ok we merge it with an issue on re-adding JDK8 to CI, unless it's doable with the downgrade of the dependent library.

[reta]

I think this should be a blocker. Can we downgrade? We need at least some CI on JDK8, anything even a basic integration test would be enough.

We could downgrade but to unsupported version (which is not good), alliteratively we could try to use other way to get the git details needed, I will look further

[dblock]

@VachaShah or @Bukhtawar ?

[VachaShah]

I am fine with merging this, thank you @reta for adding this! A few TODOs:

1. We can add the restored support details to the client documentation. For example, here https://github.com/opensearch-project/opensearch-java/blob/main/DEVELOPER_GUIDE.md.
2. As @dblock mentioned, CI with JDK-8.

[reta]

As @dblock mentioned, CI with JDK-8.

Was trying to pull it off, but there are 3 blockers (previously I thought there is only 1 but it turns out Gradle reports issues one at a time):

1. grgit-gradle - this one could be rewritten
2. spotless - we need at least 6.23.x for JDK-21 but it seems like 6.11.x was the last one that supported JDK-8
3. OpenSearch build tools (OpenSearch Gradle plugins) - needs JDK-11

So I am not sure what could we do here besides enforcing the target / source level

[reta]

1. . For example, here https://github.com/opensearch-project/opensearch-java/blob/main/DEVELOPER_GUIDE.md.

Thanks @VachaShah, we have this documented in the COMPATIBILITY.md, so updated the versions there

[dblock]

So I am not sure what could we do here besides enforcing the target / source level

Open a GitHub issue?

[reta]

Open a GitHub issue?

For grgit and spotless decisions to move baselines to JDK-11 were deliberate (I could link the related issues if you are curious), so I don't think we should be opening an issue here. For OpenSearch build tools we probably could try to go with JDK 8 baseline but that would not solve the problem at large

[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/backport-2.x 2.x
# Navigate to the new working tree
pushd ../.worktrees/backport-2.x
# Create a new branch
git switch --create backport/backport-767-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 ff5e0a2d5f04acb4c11c3217b6e8fc71161a2a4b
# Push it to GitHub
git push --set-upstream origin backport/backport-767-to-2.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-767-to-2.x.

[dblock]

Ok, I merged this, will need a manual backport - let's try to release a version that restored JDK8 support?